Road Trips in the Model S

For quite some time Tesla Toronto has been promising to put an HPC in Kingston, which would make Ottawa/Toronto and Montreal/Toronto travel much easier than it is now. But it has never happened. Last time I talked to them they were waffling, because they didn't want to spend the money and not have it be useful for Model S. Very disappointing. Ironically, the secrecy concerning the Model S charge port is interfering with rolling out infrastructure for charging Tesla cars!

The current situation is a little awkward. The place we've found to charge is an RV campground that is itself at the extreme edge of range to Toronto. So we have to fully top up a Range Mode charge, which takes a long time, and drive slower than the average traffic. It's inconvenient enough that my wife would rather take the ICE car.

So that got me thinking about the Model S. Would its extra range really allow a non-stop trip? And if not, how much charge time would be required?

There is more than a little guesswork in these numbers... feel free to comment.

If it takes 3.5 hours to charge a Roadster on an HPC; that gives ballpark 100 km / 64 miles per charging hour. On a NEMA 14-50 that's more like 55 km / 34 miles.

For a Model S, with a 95 kWh pack and a nominal 300 miles range, the charging is slower. At HPC levels we're talking 72 km / 45 miles per charging hour. That means using an HPC for a Model S is comparable to using a NEMA 14-50 on a Roadster. Full charge time on an HPC would be on the order of 6.3 hours.

My typical trip to Toronto is very close to 400 km / 250 miles (stopping in the West end). Okay, less than 300 miles, that's good, right?

Not so fast. The 416/401 highways have 100 kph speed limits, with trucks going 105 kph (speed limiters) and cars ranging from 110 kph to 120 kph. Driving at 100 kph is pretty scary, with all those trucks tailgating and passing you. So 105 kph is actually a practical minimum, IMHO.

I hacked up Tesla's Roadster efficiency spreadsheet to try and predict Model S performance, using what little information we currently have available. Take the following with a grain of salt:

90 kph / 55 mph --> 480 km / 300 miles range

100 kph / 62 mph --> 419 km / 262 miles range

105 kph / 66 mph --> 386 km / 241 miles range

110 kph / 69 mph --> 363 km / 227 miles range

120 kph / 75 mph --> 325 km / 203 miles range

The upshot is, if I'm willing to drive right at the speed limit, I can get there in one go -- just barely -- but it isn't a comfortable speed on that highway. Any faster than 100 kph and I'm going to need some electrons. Well, if I drove 105 kph and drafted trucks all the way we would probably make it. On the bright side, if we do stop to charge then an hour on an HPC would probably be enough. That's a reasonably convenient lunch stop. Of course this all depends on actually having an HPC available.

One thing I hadn't considered before -- a longer trip might actually be faster in the Roadster. It takes a lot less time to charge than the Model S. Once you've depleted your ESS the trip is pretty much dominated by the charge time.

Of course a DC fast charger would make travel in the Model S quite painless. The question is, will we have them? So far we don't have any infrastructure at all.

I think you underestimated the potential of charging Model S from a source as capable as a Tesla HPC.

HPC output is 16,8kW. With charging efficiency around 90%, this should give you 15kWh per hour of charging, as long as you are below 80% SoC. 15kWh are approx 1/6 of battery, hence 80km/50 miles.

The trouble is of course, with a "modular" charging port architecture like rumored, no one knows what kind of charging device will serve most Model S cars on the street. I do hope adapters can be switched in the field. Otherwise, every Model S would be outfitted for the charging structure around its home, making road trips a major nuisance.

For road trips, it all comes back to L3 fast charging infrastructure with a standardized port. Sigh.

I looked into alternative routes for my specific situation. I could drive on the two-lane Highway 7 instead. The speed limit is 80 kph and cars travel between 80 and 100 kph. At 80 or 90 kph there would be no problem making the trip without charging. It will take perhaps an extra hour of driving to make the trip, so in terms of total time it's probably a wash if there's an HPC available along the 401.

In terms of the trip, there are pro's and con's. Highway 7 can be a nicer drive, but it has relatively few passing opportunities so it can be tedious, especially if it's busy. In bad weather the 401 is a much safer drive.

That said, I think deployment of fast DC charge stations could make a huge difference in the uptake of EVs in general, and the Model S in particular. You could drive for three hours, then take a 45 minute break, then get back on the road. At that pace there wouldn't be a huge difference in travel time between a Model S and an ICE, assuming you want to take periodic breaks.

That said, I think deployment of fast DC charge stations could make a huge difference in the uptake of EVs in general, and the Model S in particular. You could drive for three hours, then take a 45 minute break, then get back on the road. At that pace there wouldn't be a huge difference in travel time between a Model S and an ICE, assuming you want to take periodic breaks.

Click to expand...

And actually often less than 45 minutes. My longest regular trip is around 240 miles, which I will normally drive at around 75mph. Using the table above, I would only need to charge for about 10 minutes [What's the EV equivalent of a 'splash and dash'?]. The ICE paradigm of always filling a car to full needn't apply

So that got me thinking about the Model S. Would its extra range really allow a non-stop trip? And if not, how much charge time would be required?

One thing I hadn't considered before -- a longer trip might actually be faster in the Roadster. It takes a lot less time to charge than the Model S. Once you've depleted your ESS the trip is pretty much dominated by the charge time.

Of course a DC fast charger would make travel in the Model S quite painless. The question is, will we have them? So far we don't have any infrastructure at all.

Click to expand...

As per my previous post, this got me wondering. I've used the following assumptions to produce a spreadsheet and a graph showing the time saving of using a Model S against a Roadster:

90kWH battery in Model S, 53 in Roadster. 100% full on departure, empty on arrival.
Power consumption / range as per the Tesla motors blog post on Roaster Efficiency. For the S I factored the range by the ration of actual/ideal found in the Roadster at various speeds.
Charging at 15kW into the ESS.

This shows that it's the lower power consumption of the Roadster that dominates once the additional range of the S is passed. At 90mph the Roadster is faster for journeys over 260 miles, at 60mph it's 400 miles before the break-even point.
This is independent of the actual distribution of chargers, it just assumes that it is not necessary to slow down to extend range enough to reach one. It also assumes no time is lost faffing around getting the charger to work (!).

The second chart is the travel time for the Roadster. It shows that once the initial range is exceeded, there is little difference between travelling at speeds between 55 and 65 mph. Speeds above that become progressively slower. 90mph takes around 20% longer than 60mpg for long journeys.